CN108221053A - The preparation of novel nonlinear optical crystal and purposes - Google Patents

Abstract

The present application discloses an inorganic compound, characterized in that the chemical formula of the inorganic compound is: M ₂ Ge(IO ₃ ) ₆ wherein M is Li and/or Na; the inorganic compound belongs to the hexagonal crystal system, and the space group is P6 ₃ , and the unit cell parameter is α=β=90°, γ=120°, Z=1. The inorganic compound exhibits a strong frequency-doubling effect, and its powder SHG coefficient exceeds 15 times that of KH ₂ PO ₄ (KDP), up to 32 times; measured under 2.05 μm laser irradiation, its powder SHG coefficient is KTiOPO ₄ (KTP ) crystal 2 or 0.8 times, and can achieve phase matching, is a nonlinear optical material with potential application value.

Description

Preparation and Application of Novel Nonlinear Optical Crystal

technical field

The application relates to inorganic compounds, their preparation and application as nonlinear optical crystals, belonging to the field of inorganic materials.

Background technique

Nonlinear optical crystals are a class of functional materials widely used in the field of optoelectronic technology, which can realize laser frequency conversion, modulation of laser intensity and phase, and holographic storage of laser signals.

The nonlinear optical crystals currently used in practice include LiB ₃ O ₅ (LBO), β-BaB ₂ O ₄ (BBO), KH ₂ PO ₄ (KDP), KTiOPO ₄ (KTP), α-LiIO ₃ and so on. With the development of laser technology and the emergence of tunable lasers, nonlinear optical devices have developed rapidly, and laser frequency doubling, frequency mixing, parametric oscillation and amplification; electro-optic modulation, deflection, Q-switching and photorefractive devices have appeared one after another. The above studies and applications have put forward more and higher requirements for physical and chemical properties of nonlinear optical materials, and also promoted the rapid development of nonlinear optical materials. Second-order nonlinear optical crystal materials must have a noncentrosymmetric structure.

Contents of the invention

According to one aspect of the present application, a novel inorganic compound is provided, which exhibits a strong frequency-doubling effect, and its powder SHG coefficient is more than 15 times that of KH ₂ PO ₄ (KDP), up to 32 times; at 2.05 μm The powder SHG coefficient measured under laser irradiation is 2 or 0.8 times that of KTiOPO ₄ (KTP) crystal, and can achieve phase matching. It is a nonlinear optical material with potential application value.

The inorganic compound is characterized in that the chemical formula of the inorganic compound is:

M ₂ Ge(IO ₃ ) ₆

Wherein, M is Li and/or Na;

The inorganic compound belongs to the hexagonal crystal system, the space group is P6 ₃ , and the unit cell parameter is α=β=90°, γ=120°, Z=1.

The ultraviolet absorption cut-off wavelength of the inorganic compound is 250-350 nm.

As an implementation, when M=Li, Li ₂ Ge(IO ₃ ) ₆ has a high transmittance in the spectral range of 310-2500 nm, and the UV absorption cut-off wavelength is between 315-325 nm (about 321 nm).

As an implementation, when M=Na, the crystal of Na ₂ Ge(IO ₃ ) ₆ has a wide transmission range, a high transmittance in the spectral range of 250-2500nm, and an ultraviolet absorption cut-off wavelength between 260-2500nm. 275 (about 267nm).

In the crystal structure of the inorganic compound, each asymmetric unit contains one M, one Ge, one I and three O atoms. Each Ge atom is connected with 6 O atoms to form a GeO ₆ octahedron, while each I atom is connected with 3 O atoms to form an IO ₃ triangular pyramid, and the 6 IO ₃ triangular pyramids are connected in a GeO ₆ octahedron by monodentate coordination A 0-dimensional [Ge(IO ₃ ) ₆ ] ^2- anion group is formed. M atoms fill the gaps between [Ge(IO ₃ ) ₆ ] ^2- anion groups; the lone pairs of electrons in IO ₃ ^- are arranged in the same direction along the c-axis, and this arrangement is conducive to increasing the polarity of the compound. properties, thereby enhancing its nonlinear optical coefficient.

As an embodiment, in the chemical formula of the inorganic compound, M is Li, and the unit cell parameter is α=β=90°, γ=120°, Z=1.

The crystal structure of Li ₂ Ge(IO ₃ ) ₆ is shown in Fig. 1 . Figure 1 is a schematic projection of the crystal structure along the c-axis direction. Each asymmetric unit contains one Li, one Ge, one I and three O atoms. Each Ge atom is connected with 6 O atoms to form a GeO ₆ octahedron, while each I atom is connected with 3 O atoms to form an IO ₃ triangular pyramid, and the 6 IO ₃ triangular pyramids are connected in a GeO ₆ octahedron by monodentate coordination A 0-dimensional [Ge(IO ₃ ) ₆ ] ^2- anion group is formed. Li atoms fill the gaps between the [Ge(IO ₃ ) ₆ ] ^2- anion groups. It can be seen from Fig. 1 that the arrangement of the lone pair of electrons in IO ₃ ^- along the c-axis direction is basically the same. This arrangement is beneficial to increase the polarity of the compound, thereby enhancing its nonlinear optical coefficient.

As an embodiment, in the chemical formula of the inorganic compound, M is Na, and the unit cell parameter is α=β=90°, γ=120°, Z=1.

The crystal structure of Na ₂ Ge(IO ₃ ) ₆ is shown in Fig. 2 . Fig. 2 is a schematic projection of the crystal structure along the c-axis direction. Each asymmetric unit contains one Na, one Ge, one I and three O atoms. Each Ge atom is connected with 6 O atoms to form a GeO ₆ octahedron, while each I atom is connected with 3 O atoms to form an IO ₃ triangular pyramid, and the 6 IO ₃ triangular pyramids are connected in a GeO ₆ octahedron by monodentate coordination A 0-dimensional [Ge(IO ₃ ) ₆ ] ^2- anion group is formed. Na atoms fill the gaps between [Ge(IO ₃ ) ₆ ] ^2- anion groups. It can be seen from Fig. 2 that the arrangement of the lone pair of electrons in IO ₃ ^- along the c-axis direction is basically the same. This arrangement is beneficial to increase the polarity of the compound, thereby enhancing its nonlinear optical coefficient.

According to yet another aspect of the present application, there is provided a method for preparing the inorganic compound, which is characterized in that the method is prepared by a hydrothermal method, and the raw material mixture containing M element, germanium element, iodine element and water is crystallized at 180°C to 260°C. crystallized at the melting temperature;

In the raw material mixture, the molar number of the M element, the molar number of the germanium element, the molar number of the iodine element and the water volume ratio are:

M: Ge: I: Water = 1-10 mol: 1 mol: 1-20 mol: 1-50 L.

Preferably, in the raw material mixture, the molar number of M element, the molar number of germanium element, the molar number of iodine element and the water volume ratio are:

M: Ge: I: water = 5mol: 1mol: 2-10mol: 1-5L.

Preferably, the crystallization temperature is 180°C-250°C, and the crystallization time is not less than 24 hours.

Further preferably, the crystallization time is 24-260 hours.

Preferably, after the crystallization is completed, the temperature is lowered to room temperature at a cooling rate of 0.5-13° C./hour, and the obtained solid is separated and washed to obtain the inorganic compound.

Optionally, in the raw material mixture, the M element comes from a lithium-containing compound and/or a sodium-containing compound.

Preferably, the lithium-containing compound is at least one selected from lithium nitrate, lithium chloride, lithium fluoride, lithium oxide, lithium carbonate, and lithium dihydrogen phosphate. Further preferably, the lithium salt is lithium carbonate.

Preferably, the sodium-containing compound is at least one selected from sodium nitrate, sodium chloride, sodium fluoride, sodium oxide, sodium carbonate, and sodium dihydrogen phosphate. Further preferably, the lithium salt is sodium carbonate.

Preferably, in the raw material mixture, the germanium element comes from at least one of germanium nitrate, germanium chloride and germanium oxide. Further preferably, the germanium element comes from germanium oxide.

Preferably, in the raw material mixture, the iodine element comes from at least one of diiodine pentoxide, iodic acid, and periodic acid. Further preferably, the iodine element comes from I ₂ O ₅ .

According to still another aspect of the present application, an application of the inorganic compound as a nonlinear optical crystal material is provided. The nonlinear optical crystal material is characterized in that it contains any of the above-mentioned inorganic compound crystals and/or inorganic compound crystals prepared according to any of the above-mentioned methods.

When M=Li, Li ₂ Ge(IO ₃ ) ₆ crystals output strong 532nm green light under 1064nm laser irradiation, and its powder SHG coefficient is 32 times that of KH ₂ PO ₄ (KDP), and under 2.05μm laser irradiation It is measured that its powder SHG coefficient is 2.0 times that of KTiOPO ₄ (KTP) crystal, and both can achieve phase matching.

When M=Na, Na ₂ Ge(IO ₃ ) ₆ crystals output strong 532nm green light under 1064nm laser irradiation, and its powder SHG coefficient is 15 times that of KH ₂ PO ₄ (KDP), and under 2.05μm laser irradiation It is measured that the SHG coefficient of its powder is 0.8 times that of KTiOPO ₄ (KTP) crystal, and both can achieve phase matching.

According to yet another aspect of the present application, there is provided a laser frequency converter, which is characterized in that it comprises any of the above inorganic compound crystals and/or inorganic compounds prepared according to any of the above methods.

The beneficial effects of this application include but are not limited to:

(1) This application provides a new inorganic compound, which exhibits a strong frequency-doubling effect, and its powder SHG coefficient exceeds 15 times that of KH ₂ PO ₄ (KDP), up to 32 times; at 2.05 μm The powder SHG coefficient measured under laser irradiation is 2 or 0.8 times that of KTiOPO ₄ (KTP) crystal, and can achieve phase matching. It is a nonlinear optical material with potential application value.

(2) The inorganic compound provided in this application has a very high transmittance in the spectral range of 310-2500nm, and its ultraviolet absorption cut-off wavelength is about 321nm.

(3) The inorganic compound provided by this application can be stable up to 416°C.

(4) The present application also provides a method for preparing the inorganic compound crystal. A colorless M ₂ Ge(IO ₃ ) ₆ crystal is grown by hydrothermal crystallization. The process of the method is simple, and the inorganic compound M ₂ Ge(IO ₃ ) ₆ crystal material with high purity and high crystallinity can be obtained.

Description of drawings

Fig. 1 is a schematic diagram of the crystal structure of Li ₂ Ge(IO ₃ ) ₆ crystal.

Fig. 2 is a schematic diagram of the crystal structure of Na ₂ Ge(IO ₃ ) ₆ crystal.

Figure 3 is a comparison of the X-ray diffraction pattern obtained by fitting the crystal structure of sample Li-1 ^# based on single crystal X-ray diffraction analysis and the pattern obtained by X-ray diffraction test of sample 1 ^# after being ground into powder.

Figure 4 is a comparison of the X-ray diffraction pattern obtained by fitting the crystal structure of sample Na-1 ^# based on single crystal X-ray diffraction analysis and the pattern obtained by X-ray diffraction test of sample 1 ^# after being ground into powder.

Fig. 5 is the ultraviolet-visible-near-infrared diffuse reflectance spectrum of sample Li-1 ^# .

Figure 6 is the UV-Vis-NIR diffuse reflectance spectrum of sample Na-1 ^# .

Fig. 7 is the thermogravimetric diagram of sample Li-1 ^# .

Fig. 8 is the thermogravimetric diagram of sample Na-1 ^# .

Detailed ways

The present application is described in detail below in conjunction with the examples, but the present application is not limited to these examples.

Unless otherwise specified, the raw materials and reagents used in this application were purchased commercially and used directly without treatment, and the instruments and equipment used used the scheme and parameters recommended by the manufacturer.

The preparation of embodiment 1 sample Li-1 ^# ～sample Li-5 ^#

Lithium source, germanium source, iodine source and water are mixed into raw materials according to a certain molar ratio, placed in a polytetrafluoroethylene-lined high-pressure reactor, and then heated to the crystallization temperature, and kept at this temperature for a period of time, The temperature of the system was lowered to room temperature at a certain cooling rate. After suction filtration and washing, a colorless rod-shaped crystal sample was obtained, which was the sample of the inorganic compound crystal.

The sample number, type and amount of raw materials, crystallization temperature and holding time, and cooling rate are shown in Table 1.

Table 1

Crystal structure analysis of embodiment 2 sample Li-1 ^# ~ sample Li-5 ^#

The structures of samples Li-1 ^# ~ Li5 ^# were analyzed by single crystal X-ray diffraction and powder X-ray diffraction.

The single crystal X-ray diffraction was carried out on a SuperNova CCD type X-ray single crystal diffractometer of Agilent Corporation, USA. The data collection temperature is 293K, and the diffraction light source is the Mo-Kα ray monochromated by graphite The scanning method is ω-2θ; the data is processed by the Multi-Scan method for absorption correction. Structural analysis was completed with the SHELXTL-97 program package; the position of the heavy atoms was determined by the direct method, and the coordinates of the remaining atoms were obtained by the differential ^Fourier synthesis method; the coordinates of all atoms and the anisotropic thermal parameter.

Powder X-ray diffraction was carried out on the Miniflex II X-ray powder diffractometer of Japan Rigaku Co., Ltd. (RIGAKU). The test conditions were fixed target monochromatic light source Cu-Kα, wavelength The voltage and current are 30kV/15A, the scanning range is 5-65°, and the scanning step is 0.02°.

Among them, the single crystal X-ray diffraction results show that samples 1 ^# to 5 ^# have chemical formulas of Li ₂ Ge(IO ₃ ) ₆ , belong to hexagonal crystal system, space group is P6 ₃ , and unit cell parameters are α=β=90°, γ=120°. Its crystal structure is shown in Figure 1, which is a schematic projection of the crystal structure along the c-axis direction. It can be seen that each asymmetric unit contains one Li, one Ge, one I and three O atoms. Each Ge atom is connected with 6 O atoms to form a GeO ₆ octahedron, while each I atom is connected with 3 O atoms to form an IO ₃ triangular pyramid, and the 6 IO ₃ triangular pyramids are connected in a GeO ₆ octahedron by monodentate coordination A 0-dimensional [Ge(IO ₃ ) ₆ ] ^2- anion group is formed. Li atoms fill the gaps between the [Ge(IO ₃ ) ₆ ] ^2- anion groups. From Figure 1, we can see that the lone pairs of electrons in IO ₃ ^- are basically aligned along the c-axis direction. This arrangement is beneficial to increase the polarity of the compound, thereby enhancing its nonlinear optical coefficient.

The results of powder X-ray diffraction showed that samples Li-1 ^# ~ Li-5 ^# had basically the same peak positions in the XRD spectrum, and the peak intensities of different samples were slightly different.

Take the sample Li-1 ^# as a typical representative, which belongs to the hexagonal crystal system, the space group is P6 ₃ , and the unit cell parameters are α=β=90°, γ=120°, Z=1. The single crystal analysis results are shown in Table 2:

Table 2

Taking the sample Li-1 ^# as a typical representative, as shown in Figure 3, according to the crystal structure analyzed by its single crystal X-ray diffraction, the X-ray diffraction pattern obtained by fitting is consistent with the X-ray diffraction pattern after the sample Li-1 ^# is ground into powder The spectrum obtained by testing, the peak position and peak intensity are consistent. It shows that the obtained samples are of high purity.

Frequency doubling test experiment and result of embodiment 3 sample Li-1 ^#

Taking the sample Li-1 ^# as a typical representative, the frequency doubling test was carried out on Li ₂ Ge(IO ₃ ) ₆ .

The specific steps are as follows: using the Q-switched Nd:YAG solid-state lasers with frequency converters to generate lasers with wavelengths of 1064 nm and 2.05 μm respectively as the fundamental frequency light, irradiate the crystal powder to be tested, and use the photomultiplier tube to detect the generated secondary light. Harmonics, use an oscilloscope to display the strength of the harmonics. Use a standard sieve to sieve the crystal sample to be tested into crystals with different particle sizes, the particle sizes are 25-45 μm, 45-53 μm, 53-75 μm, 75-105 μm, 105-150 μm, 150-210 μm, 210-300 μm. Observe the change trend of the multiplier signal with the particle size, and judge whether it can achieve phase matching. Under the same test conditions, compare the intensity of the second harmonic generated by the sample to be tested with the intensity of the second harmonic generated by the reference crystal KH ₂ PO ₄ (KDP) and KTiOPO ₄ (KTP), so as to obtain the frequency doubling of the sample The relative size of the effect.

The test results show that the powder SHG coefficient of compound Li ₂ Ge(IO ₃ ) ₆ under 1064nm laser irradiation is 32 times that of KH ₂ PO ₄ (KDP), and under 2.05μm laser irradiation, its powder SHG coefficient is KTiOPO ₄ ( KTP) crystal twice, and can achieve phase matching.

The diffuse reflectance absorption spectrum test of embodiment 4 sample Li-1 ^#

Taking the sample Li-1 ^# as a typical representative, the diffuse reflectance absorption spectrum test of Li ₂ Ge(IO ₃ ) ₆ was carried out on a Lambda-950 UV-Vis-Near-Infrared Spectrophotometer of Perkin-Elmer Company of the United States. The crystal sample was ground into powder, and BaSO ₄ was used as the reference substrate. The test results are shown in Figure 5, which shows that the compound Li ₂ Ge(IO ₃ ) ₆ crystal has a wide transmission range, high transmittance in the spectral range of 310-2500nm, and the UV absorption cut-off wavelength is about 321nm.

The thermogravimetric analysis of the sample of embodiment 5 sample Li-1 ^#

Taking sample Li-1 ^# as a typical representative, Li ₂ Ge(IO ₃ ) ₆₂ was subjected to thermogravimetric analysis on a STA449F3 thermogravimetric analyzer from NETZSCH, Germany, and the results are shown in Figure 7. It can be seen from the figure that the crystal of Li ₂ Ge(IO ₃ ) ₆ can be stable up to 416°C.

The preparation of embodiment 6 sample Na-1 ^# ～sample Na-5 ^#

Sodium source, germanium source, iodine source and water are mixed into raw materials according to a certain molar ratio, placed in a polytetrafluoroethylene-lined high-pressure reactor, and then heated to the crystallization temperature, and kept at this temperature for a period of time, The temperature of the system was lowered to room temperature at a certain cooling rate. After suction filtration and washing, a colorless plate-like crystal sample was obtained, which was the sample of the inorganic compound crystal.

The sample number, type and amount of raw materials, crystallization temperature and holding time, and cooling rate are shown in Table 3.

table 3

Crystal structure analysis of embodiment 7 sample Na-1 ^# ～sample Na-5 ^#

The structures of samples Na-1 ^# ~Na-5 ^# were analyzed by single crystal X-ray diffraction and powder X-ray diffraction.

The single crystal X-ray diffraction was carried out on a SuperNova CCD type X-ray single crystal diffractometer of Agilent Corporation, USA. The data collection temperature is 293K, and the diffraction light source is the Mo-Kα ray monochromated by graphite The scanning method is ω-2θ; the data is processed by the Multi-Scan method for absorption correction. Structural analysis was completed with the SHELXTL-97 program package; the position of the heavy atoms was determined by the direct method, and the coordinates of the remaining atoms were obtained by the differential ^Fourier synthesis method; the coordinates of all atoms and the anisotropic thermal parameter.

Powder X-ray diffraction was carried out on the Miniflex II X-ray powder diffractometer of Japan Rigaku Co., Ltd. (RIGAKU). The test conditions were fixed target monochromatic light source Cu-Kα, wavelength The voltage and current are 30kV/15A, the scanning range is 5-65°, and the scanning step is 0.02°.

Among them, the single crystal X-ray diffraction results show that the samples Na-1 ^# ~Na-5 ^# have the chemical formula Na ₂ Ge(IO ₃ ) ₆ , belong to the hexagonal crystal system, the space group is P6 ₃ , and the unit cell parameters are α=β=90°, γ=120°, Z=1. Its crystal structure is shown in Figure 2, which is a schematic projection of the crystal structure along the c-axis direction. It can be seen that each asymmetric unit contains one Na, one Ge, one I and three O atoms. Each Ge atom is connected with 6 O atoms to form a GeO ₆ octahedron, while each I atom is connected with 3 O atoms to form an IO ₃ triangular pyramid, and the 6 IO ₃ triangular pyramids are connected in a GeO ₆ octahedron by monodentate coordination A 0-dimensional [Ge(IO ₃ ) ₆ ] ^2- anion group is formed. Na atoms fill the gaps between [Ge(IO ₃ ) ₆ ] ^2- anion groups. From Fig. 2 we can see that the arrangement of the lone pair of electrons in IO ₃ ^- along the c-axis direction is basically the same. This arrangement is beneficial to increase the polarity of the compound, thereby enhancing its nonlinear optical coefficient.

The results of powder X-ray diffraction showed that the peak positions of samples Na-1 ^# ~ Na-5 ^# were basically the same in the XRD spectrum, and the peak intensities of each sample were slightly different.

Take the sample Na-1 ^# as a typical representative, which belongs to the hexagonal crystal system, the space group is P6 ₃ , and the unit cell parameters are α=β=90°, γ=120°, Z=1. The single crystal analysis results are shown in Table 4:

Table 4

Taking sample Na-1 ^# as a typical representative, as shown in Figure 4, according to the crystal structure analyzed by its single crystal X-ray diffraction, the X-ray diffraction pattern obtained by fitting is the same as that of sample Na-1 ^# after grinding into powder X-ray diffraction The spectrum obtained by testing, the peak position and peak intensity are consistent. It shows that the obtained samples are of high purity.

The frequency doubling test experiment and result of embodiment 8 sample Na-1 ^#

Taking the sample Na-1 ^# as a typical representative, the frequency doubling test was carried out on Na ₂ Ge(IO ₃ ) ₆ .

The specific steps are as follows: using the Q-switched Nd:YAG solid-state lasers with frequency converters to generate lasers with wavelengths of 1064 nm and 2.05 μm respectively as the fundamental frequency light, irradiate the crystal powder to be tested, and use the photomultiplier tube to detect the generated secondary light. Harmonics, use an oscilloscope to display the strength of the harmonics. Use a standard sieve to sieve the crystal sample to be tested into crystals with different particle sizes, the particle sizes are 25-45 μm, 45-53 μm, 53-75 μm, 75-105 μm, 105-150 μm, 150-210 μm, 210-300 μm. Observe the change trend of the multiplier signal with the particle size, and judge whether it can achieve phase matching. Under the same test conditions, compare the intensity of the second harmonic generated by the sample to be tested with the intensity of the second harmonic generated by the reference crystal KH ₂ PO ₄ (KDP) and KTiOPO ₄ (KTP), so as to obtain the frequency doubling of the sample The relative size of the effect.

The test results show that the powder SHG coefficient of compound Na ₂ Ge(IO ₃ ) ₆ under 1064nm laser irradiation is 15 times that of KH ₂ PO ₄ (KDP), and under 2.05μm laser irradiation, its powder SHG coefficient is KTiOPO ₄ ( KTP) crystal 0.8 times, and can achieve phase matching.

The diffuse reflection absorption spectrum test of embodiment 9 sample Na-1 ^#

Taking the sample Na-1 ^# as a typical representative, the diffuse reflectance absorption spectrum test of Na ₂ Ge(IO ₃ ) ₆ was carried out on a Lambda-950 UV-Vis-Near-Infrared Spectrophotometer of Perkin-Elmer Company in the United States. The crystal sample was ground into powder, and BaSO ₄ was used as the reference substrate. The test results are shown in Figure 6, which shows that the crystal of the compound Na ₂ Ge(IO ₃ ) ₆ has a wide transmission range, a high transmittance in the spectral range of 250-2500nm, and an ultraviolet absorption cut-off wavelength of about 267nm.

The thermogravimetric analysis of embodiment 10 sample Na-1 ^#

Taking the sample Na-1 ^# as a typical representative, the thermogravimetric analysis of Na ₂ Ge(IO ₃ ) ₆ was carried out on the STA449F3 thermogravimetric analyzer of NETZSCH, Germany, and the results are shown in Fig. 8 . It can be seen from the figure that the crystal of Na ₂ Ge(IO ₃ ) ₆ can be stable up to 410°C.

The above are only a few embodiments of the application, and do not limit the application in any form. Although the application is disclosed as above with preferred embodiments, it is not intended to limit the application. Any skilled person familiar with this field, Without departing from the scope of the technical solution of the present application, any changes or modifications made using the technical content disclosed above are equivalent to equivalent implementation cases, and all belong to the scope of the technical solution.

Claims (10)

1. a kind of inorganic compound, which is characterized in that the chemical formula of the inorganic compound is：

M₂Ge(IO₃)₆

Wherein, M is Li and/or Na；

The inorganic compound belongs to hexagonal crystal system, space group P6₃, cell parameter is α=β=90 °, γ=120 °, Z=1.

2. inorganic compound according to claim 1, which is characterized in that the UV absorption cut-off wave of the inorganic compound It grows between 250~350nm.

3. inorganic compound according to claim 1, which is characterized in that M is Li in the chemical formula of the inorganic compound, Cell parameter is α=β=90 °, γ=120 °, Z=1； Or

M is Na in the chemical formula of the inorganic compound, and cell parameter is α=β=90 °, γ=120 °, Z=1.

4. the preparation method of any one of a kind of claims 1 to 3 inorganic compound, which is characterized in that using hydro-thermal legal system Standby, by the raw mixture containing M element, Germanium, iodine and water, crystallization obtains under 180 DEG C~260 DEG C crystallization temperatures It arrives；

In the raw mixture, the molal quantity of M element, the molal quantity of Germanium, the molal quantity of iodine and water volume ratio For：

M：Ge：I：Water=1~10mol：1mol：1~20mol：1~50L；

Preferably, M：Ge：I：Water=5mol：1mol：2~10mol：1~5L.

5. according to the method described in claim 3, it is characterized in that, the crystallization temperature be 180 DEG C~250 DEG C, crystallization time No less than 24 hours；

Preferably, the crystallization time is 24~260 hours.

6. the method according to claim 3 or 5, which is characterized in that in the raw mixture, M element carrys out self-contained lithiumation Close object and/or compounds containing sodium；

Preferably, the lithium-containing compound is selected from least one of lithium nitrate, lithium chloride, lithium fluoride, lithia, lithium carbonate； It is further preferred that the lithium salts is lithium carbonate；

Preferably, the compounds containing sodium is selected from least one of sodium nitrate, sodium chloride, sodium fluoride, sodium oxide molybdena, sodium carbonate； It is further preferred that the lithium salts is sodium carbonate.

7. according to the method described in claim 3, it is characterized in that, in the raw mixture, Germanium is from nitric acid germanium, chlorine Change at least one of germanium, germanium oxide；

Preferably, the Germanium comes from germanium oxide.

8. according to the method described in claim 3, it is characterized in that, in the raw mixture, iodine is from five oxidations two At least one of iodine, acid iodide, periodic acid；

Preferably, the iodine comes from I₂O₅。

9. inorganic compound described in claims 1 or 2, the nothing being prepared according to any one of claim 3 to 8 the method Application of at least one of the machine compound as non-linear optical crystal material.

10. a kind of laser frequency converter, which is characterized in that comprising described in claims 1 or 2 inorganic compound, according to power Profit requires one kind in inorganic compound prepared by any one of 3 to 8 the methods.